I own a 72 Chevy C20 truck. I recently installed a post head unit from custom auto sound in an effort to keep a vintage looking interior, along with two pioneer 6.5s and a dual voice coil 4X10. Those components by themselves work fine. Last night I added a Kenwood subwoofer/amp unit consisting of two 6.5” subs in a small factory box and a built in 150W amp. When the truck is idling the subs work intermittently. Each time the bass hits it’s like a switch is flipped on and off during the speakers oscillation. When the engine is not running and the key is turned on the subs sound great. Also when engine RPMs are increased (highway speeds) the unit sounds great. The truck has a new 55 amp alternator which is more than the factory 42 amp that came with the truck. Thanks in advance for all the help.
Because the subs and amp are all in one box and assembled that way from the factory (see link below) I can only assume that polarity is correct. There is a slight amount of engine noise in the other speakers when listening to certain radio stations now that you mention it. I guess I'll have to diagnose that first. Any suggestions?
https://www.bestbuy.com/site/olspage.jsp?skuId=7332503&type=product&productCategoryId=pcmcat54900050004&id=1118845473156
check the ground for the engine block, i have seen many older vehicles with very poor grounds for the block, that wreaked havoc with electronics installations. better yet, do the big 3 upgrade.
upgrade the wire from the engine block to chassis
upgrade the ground wire for the battery to chassis
and upgrade the power wire between alternator to the battery positive.
there is a sticky in one of the sections that goes into further detail.
found the sticky for you https://www.the12volt.com/installbay/forum_posts.asp?tid=73496&PN=1
-------------