I have the Monsoon system in my 99. It doesn't sound like anything special. My passenger door speaker plays only highs. I read about a subwoofer being included in the package, but I have none. Where would it be if I were to? Also, where is the amp located for the speakers?
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your doors should not just be playing highs. they are a mid to highrange speaker. the subs they speak of aren't a true sub and they are located next to the back seats

 

I checked yesterday. All 3 speakers work on the driver side. Only the rear most one works properly on the passenger side. Is this a common problem?

 

never heard about that before so I'd have to say no

 

You might need to replace the OEM speakers as I did on my 01 Monsoon system, you can find them on eBay, and there was a known GM part problem, so the blowout is not uncommon... The new speakers have a new coating to prevent the blowout.

Circuity City will install the door speakers for around $40, although it is not very dificult...

 

the amp is located in the back panel on the passenger side. if you take off the spare tire there are like two bolts holding the amp on.