I recently bought a 2004 Mazda 6 Wagon with 55,000 miles on it. It's been great except for one issue that has me concerned. When on a highway going 45-55 mph I push down on the accelerator, the engine shifts to a lower gear, then right before/during the shift back to a higher gear a sharp half-second squeal occurs. It doesn't happen all the time, so I'm having problems getting it diagnosed. So far the mechanic adjusted the serpentine belt, but the engine did it on the way home from the garage, so I am pretty sure that wasn't the problem.

Has anyone else had this issue, or does anyone have any ideas what it could be?

 

Mine does this too, and I'm pretty sure that is has something to do with the a/c unit. This is due to the fact that when the a/c is turned off, I never get this noise, but when it's turned on it happens fairly consistantly. The sound you are hearing I know for a fact is the belt slipping, because there isn't much else I know of that can make that ungodly squeel. However, this seems to be more of a minor annoyance than any real problem. The only thing I can figure, is that the A/C unit has a system that disengages the pully (allows it to spin free) when you gun the engine to free up power for passing, then when you let off it re-engages and the sudden resistance causes the belt to slip for a second resulting in our squeel. I do not know for certain that this is the case, but it makes sense to me and explains why I have not noticed a big difference in passing power with the a/c on or off.

-Cameron Keffer