hey man, read the post i made for you on the other thread carefully. you really must plan ahead and have a basic idea of what the final end product will be BEFORE you start recording or you will make some serious compromises and your sound quality will suffer.
keep this in mind - you can really only do ONE real internal bounce on the 3340 before you start seriously losing sound quality, as you have now found. there
are many ways around this, but the 3340 is the least user friendly tape deck for bouncing. the 40-4 and 80-8, which came out later in the '70s, corrected the problem by giving you close to full frequency response in SYNC mode, and it was WAY easier to operate.
here is some basic info you NEED to know: you have 3 heads on your deck, in order - ERASE, RECORD, PLAY. the tape passes by each head in that order. if you record something, it will play it back a millisecond later. this is called tape delay. when you bounce, you are literally recording FROM the play head to the record head, so there will be a delay. if you bounce in SYNC mode, the RECORD HEAD is playing back the music AND recording it at the same time, so there is no delay. the problem is the record head sounds shitty when playing back, it was designed to be used as a GUIDE for you to listen to while overdubbing, not for fidelity. you can bounce in this manner if you do so strategically, like if you are doubling something or it is not very important to be full fidelity (i suggested using it for background vocals on the previous thread).
you would not have these problems with the later 4-track decks, namely the 40-4 or tascam 22-4. the 3340 can be VERY frustrating, i used to have one and moved on to the 80-8 REAL quick after going through exactly what you are right now. keep in mind your deck was designed as a quadrophonic tape deck. they made a simple mod so that your record head could play back in sync so you can overdub.
also, record to 1, 2, 4 and bounce to 3 ... trust me on this. there are a few reasons its better this way.
take advantage of having 2 decks ... use them, fidelity will be MUCH better overall.
plan it out man, you will avoid head scratching and frustration.