I was after some environment noise generator for an underground style tune I am working on and found these three free gems that I really liked.

First one is called 'Milli Vinylli' and is a vinyl noise simulator. You have different sections to control separately scratch, cracks, dust, hiss, etc. Using the 'hiss' section alone is great to simulate old cassete tapes. You can download it here:

Download Free Vinyl simulator plug-in: Milli Vinylli by Klanglabs

Second one is 'vinylusion' that does basically the same thing as the previous plugin, but it has a different way of control the noises, so I think it deserves a check too:

Vetrix / Free IDM VST Plugins / Experimental / Vinylusion / Download / Sound Designer

The third one is 'Ambient Electrical Noise Lite' from Syncersoft that generates 13 different types of electrical interferences such as hum, buzz, crackles, etc. Each one of the sounds can be adjusted through an embedded 3-band EQ. This is the free version of their full version (27 sounds) that is sold by $20.

Download Free Electrical sound plug-in: Ambient: Electrical Noise Lite by SyncerSoft