Subwoofers Smell Wierd

I have a Chevy Silverado Extended Cab Year 2001. In the backseat i have a Custom Made box that fits perfectly under my seat. It can fit 2 12's in it and my Amp is Fastened to the top of it. I previously had 2 12 inch MTX Jackhammer's in with no problems but i wanted a cleaner sounding bass. My friend sold me 2 12' inch Pioneer Shallow Mount Premier's. 400 Watts Nominal Power. My Amp is a Kicker 08ZX400.1 pushes 200 Watts RMS x 1 at 4 Ohms (400 Watts x 1 at 2 Ohms). I Installed the Subs no problems and i started driving and within minutes smelled a funky smell kind of tangy ish if that makes sense. The Subs are relatively new to my knowledge my friend has the same exact truck. ( I took his Box and Now the Subs that were in it the Pioneers.) He said he had that setup for like a month but i dont know what kind of amp he had. Ive heard that it could be the Excess Glue burning off but i doubt that. I Turned the bass boost all the way down i dont know what to do. I dont know much at all about Subwoofers and the way they work. Any Help would be appreciated thanks!!

The box is probably way to big for the shallow mount subs. Sometimes when you overwork a sub the excess glue can burn off - really hard to tell if you damaged them or not.