so i just got a tape adapter for using mp3 players w/my stock headunit...now i notice this volume/rpm independent hiss whenever i use the combo...any suggestions? occurs whether or not engine is running, at any speed, rpm or volume, whether or not the mp3 player is plugged in...

 

It's probably just your adapter/cassette. You can try cleaning the heads of the tape assembly. I used to use one but the quality just became unbearable, along with the mechanical noise associated with the tape player.

 

i'll try the cleaner next weekend. what do you suggest for hooking up to the headunit then? i used to have an airplay fm modulator but that wasn't very good sound quality...

 

those tape things last a week at best

 

The tape adapter is the cause of your problem. If you have an iPod bring the volume max level down a little bit and the hissing should go away and if you don't have an iPod I say you should invest in one once you get income tax back unless you already got it and spent it.

 

i've tried fiddling with the ipod volume, no effect...and my old tape adapter lasted 3 years...