feed back though tower speakers

[OLDGUY]

I have a pair of REV10s and a SYN 2 amp. I also have a WS420. There is feed back coming though the towers with the engine off. Amp is grounded to the battery. Head unit and WS420 are grounded to a common ground. If you turn down the gain the feed back goes down but doesn't go away. When the stereo is turned up you can't hear it. so I guess I can live with it.

[MLA]

If the equipment was purchased new, then I like to suggest that the retailer be a first line resource for setup, tuning and resolving issues like this, if they come up, There are more things to consider, then just the grounds. its only half the circuit. Where certain circuits terminate, gain settings, integrity of RCA cables, etc. 

[ibelonginprison]

It's fairly basic, but here's a halfway decent guide to troubleshooting noises:
https://www.crutchfield.com/S-sTbtAjt1ul1/learn/learningcenter/car/noise_suppressors_installation_guide.html 

https://images.crutchfieldonline.com/ImageBank/v20150824112100/learningcenter/articles/417/NoiseSuppress.pdf

[OLDGUY]

Went through the check list on crutchfields web site. The ground wire was to long. Go figure. Thanks again "ibelonginprison" and "MLA" for your help.