Passenger door speaker problem.
 

Hi, I have a 2004 Mazda 3 5 door hatchback with aftermarket Boston Acoustics Speakers all around the car. They are wired to an Alpine amp but this is besides the point. The passenger side front speaker has started to become extremely muffled when you first start the car. It goes from having no sound except rattling and static to as the car warms up, it gains sound and eventually (around 45 mins of driving) goes back to its normal good quality. My buddys 3 (same year same everything except auto) has the same problem except his gains its sound faster. If anyone could help that would be greatly appreciated!

I would have guessed it was the amp - but it could be the head unit (as i'd guess for your friends car). Sounds like a classic cold solder joint. When it gets cold it shrinks and breaks a connection, as it gets warmed up or maybe if you hit a bump or something it will connect. Since there's noise but it's muffled, i'd say it's in a pre-amp stage, since a speaker connection will usually be just on or off, not in this in-between state... though you may want to try poking at the wiring and see if anything changes, a corroded connection has the potential to do this too.
Good luck- haven't had any stereo issues on my ride so far - 07 GT

I'll agree it has something to do with the wires check em out and see what you can find