never really had my vibe sub and new 6x9s i got off steven working properly since i put them in a while back, they were fine at first, started going dodgey and whirring in tune with the engine.

i've tried another HU and it still done it, when it first happened i made a better earth, solved it for a few mins and it went back to whirring to the sound of the engine

i also had the RCA and Batt lead running down the same side, sorted that, same again.. worked for a while and went back.

any ideas?

cheers!

gunna test the earth by using some jump leads and earthing it to the battery

Have a quick search on it. Things like Alternator noise alternator whine ect ect. I have outlined it quite a bit.
If all else fails put a wire round the RCA barrels and earth them.