i just finished yesterday building a new box for my 13w7. I built to the specifications in my owners manual for a ported box (tuned to 30hz, took me a ridiculous 2 days to do it right). Playing at low volume it sounds beautiful as expected. However when i turn it up some more (not real loud, just enough to feel the sub movin) the sub begins to make a strange sound in correlation with the harder parts of the song's beat. I'm not quite sure how to describe online, but i can tell you its not a sound you would like to hear from a sub. I'm pretty sure (close to positive) that it is not clipping or anything caused by the amp. The only thing i did with the box that wasnt mentioned in the manual was i put foam padding on some of the inner walls (i was advised to do this because it supposedly makes the sub have a softer touch, makes it sound a little cleaner). Could this foam be the culprit?
thanks for any help