Replaced my RCA's today and now I have a terrible alt whine.  Never had this happen before so Ive been trying to do some research and what the problems could be.  Here's what Ive tried so far.

 

I've disconnected the RCA's and the whine goes away.

 

Plugged a factory wire back up with factory speaker and no whine

 

Disconnected the 4 channel amp from the ground block and grounded it independently at another point.

 

Since theres no whine with the factory speaker am I correct in assuming its nothing behind the head unit i.e. radio antenna, HU ground

 

Any other suggestions?

 

Also I did remove the remove and plug in the rca's while the system was running.  Just found out that this is a big no no. 

 

Im running an Alpine INE-S920HD, with a PDX-F6 & M6

It could still be the HU ground. 

 

There is a sticky at the top of this section that gives a step by step on troubleshooting noise.

If you replaced your RCAs and got the wine afterward chances are it has something to do with your RCAs. Other things it could be is a bad RCA ground in the head unit (Vey common in Pioneer head units), bad grounds, bad alternator.