Car stereo whistle noise?

-So i added a 4 channel amp to my speakers and now all of a sudden there is a whistle. It doesn't change volume, only pitch with RPM. the RCA's are run from head unit into my amp to subs then out and split into the 4 channel, is that it or could it be drawing more power than the alternator can put out?http://www.termpro.com/articles/noise.ht鈥?/a>