YES! We assume too much, when it will either cost us money or it was someone's job to do it right in the past. I think I've already said this in this forum somewhere, but when you buy a house, here in the states (and probably most anywhere), there are safety rules that the builder had to follow. In the trades, it's called following the builder's code. And things are inspected, to make sure these codes are followed. When it was a pre-existing house, everything still has to be inspected, to make sure it's "up to code", in regards to safety, before a sale can be finalized.
But, there are ways around all of this. It's sad, but if you know somebody...who knows somebody else, you can do things out of code or not fully following code. My house was remodeled before I bought it. It looked great. The ceiling was vaulted in the kitchen and a cathedral ceiling in the living room. The ceilings were originally 10 feet high, so they didn't disturb the attic, when they did that. The home owner did all of the work and his uncle was an inspector. See where this is going? Yep, while they didn't do anything themselves that could have been considered that unsafe with the electricity, they connected their wiring to the existing wiring, and that wiring was far below present day code.
This is an old shot gun house. It was built in 1935. It has actual 2X4 lumber in it and square nails. The main structural frame of this house is still quite strong. Unfortunately, it also had slat and lath walls, too...AND NO INSULATION! Back when it was built, there were no high energy bills. You just turned the heat up a little more.
When the previous owners remodeled the house, they only put insulation in rooms they put new sheet rock on. And they ran new electrical wires in those rooms, too. But, half of the house just had newly painted walls, to resemble the ones that had been remodeled, so we "assumed" the whole house had been remodeled. In fact, those were the very words that were spoken..."the whole house has been remodeled".
The electricity in the part of the house that hadn't actually been remodeled hadn't been updated or even checked for many years. And with the remodeling, that present wiring experienced vibrations and other movement that it hadn't felt...probably ever. So, some of the connections up in the attic were weakened, even if they were good connections in maybe...1950 or 1970?
I wasn't in the house 6 months before half of the electricity in the kitchen just went out, but no breaker blew. How I found it was to plug in a loud blender and then go up into the attic and start moving wires around, until I found the connection that was causing the separation and heard the blender come on. It was one of the existing connections (pre-remodel) and all they did back then was to twist the two ends of a wire together and tape it with electrical tape. There were no wire nuts and the tape was mostly rotted away. Over the years, and with vibrations and movement from the remodel in the room below, that twisted connection got loose.
Thankfully, I saw the way the electricity in the house looked very soon after the purchase. There could have been a fire, if those wires happened to get loose enough to heat up, or even arc. And if not that one, maybe one of the other existing connections. So, I redid all of the wiring in the house, taking out the old wire and putting in new. The wire itself wasn't bad as it was good 12 guage electrical wire. But, I just went with "out with the old and in with the new" thought process.
In the process of doing this, I found that in the part of the house that just had newly painted walls (the ones with slat and lath and no insulation) also had no earth ground wires at all. Oh, they put in new 3 prong outlets, but they didn't have a green wire to ground in any of them. They also didn't do that good a job of putting in the new outlets either as they reversed hot and neutral in several of them.
It really makes me wonder...if the electricity hadn't gone out in the kitchen, or if I hadn't decided to put in a studio, a little later, I might have never found these safety issues. True, they didn't do anything really illegal themselves, but they weren't qualified electricians to do the work, either. A qualified electrician wouldn't have done some of those things or left the existing wiring like that.
I won't even go into how some devices will be perfectly fine when used alone, but if you put two of them in the same system, they don't like each other and a buzz or hum develops. Maybe one of the manufacturers didn't go far enough in filtering out possible EF interference and it now is causing you headaches. But, even if they did leave out some filters to try and save some mass production money, if your electrical wiring is correct as it can by with a good earth ground and the hot and neutral wires where they should be and there are no compressors from a refrigerator or something else on the same circuit, it might not be an issue.
But, even if you have everything correct, you can still hear some strange things. Maybe the sun decided to have a few spots one day or something else totally out of human control happened to find it's way into your life. I've got an Interstate highway about 1/2 mile from my house. There are still days, while fewer and fewer in number, when I'll hear some trucker saying "breaker one nine, anybody out there got their ears on?" or something similar in my speakers. It only lasts for a few seconds, but at just the wrong moment, it could appear on my recordings.
So, don't assume someone did their job, when looking for what could be the cause of a hum or a buzz in your recording system. It's not always true. There are so many ways for someone to get around doing what they should do and what we assume they did. And sadly, even if it's not done correctly, electricity does still work and the lights will go on. But, if you assume that's because someone did it correctly, you could be mistaken.
All right seeing we are looking at all kinds of causes, I had an induced noise from a power pac plugged into the back of a piggy back plug (or double adaptor) the item with the power pac was fine but the other piece of gear, in this case a Yamaha SPX90, suddenly started to hum and have noise problems.
I also had problems in one of my early studios with the telephone exchange across the road, I was getting induced noise into the mains supply cables, this was extremely hard to get rid off and the only way was to use very good quality cables. It caused real problems whenever a single coil guitar turned up as that picked up the airborne stuff.
Just pointed this out as there is sometimes no simple answer and investigation is needed.
Go back to my answer #8 where I asked if the power point had a good earth, don't assume it does, even the house earth may be bad or non-existent. I did move into a house years ago where someone had broken the main earth cable through the roof between the main switchboard and the main earth point, just left it and did not fix it, a deadly trap for some poor person later. Fixed that and put down a better earth stake and all noise including the stereo in the lounge went away. Check the earth resistance in the house!
Alan.