Periodically, when the weather is warm (above around 85F), the brakes on our Wagon make a shuddering or rumbling sound when depressed. This happens at all speeds. Although it doesn't seem to affect the braking, we definitely sense that something bad is going on and avoid using the brakes as a consequence.

Our mechanic, who is not a dealer but is a Volvo specialist, could not detect a problem with the brakes (it also never seems to be warm on the days that we happen to bring the car by). He installed some anti-vibration parts, but this has not helped.

Would appreciate any help that might focus our mechanic on the problem.