90 740 Turbo - Major brake problems

Front inner and outer wheel bearings?

Lift up front of car, remove tire and spin wheel hub: see if there is wobble or deflection in the rotor.

Check for play / noise re: wheel bearings.

You probably have warped rotors that could have come from overheating the brakes or from the wheels not being properly torqued when the tires were replaced. Because the car is almost 20 years old the front- end may be loose and minor rotor wobble could be magnified as a result. Best to have a good Volvo mechanic take a look. If the rotors are old and have been turned once there is an excellent chance that they are too thin to be turned again.

The one problem I've had with my 740 which I've so far never been able to solve is it's tendency to warp right-front rotors. Once it could be blamed on siezed caliper slides, but those have since been fixed. Calipers were replaced at one point, tried high quality PowerDisc rotors, since then I've been using junkyard rotors and swapping when they warp. This summer I'm thinking of replacing the rubber lines, blowing compressed air through the steel lines to flush them out, and I may swap the ABS modulator since they're cheap and easy to find used, I can't think of anything else it could be that would affect just that one wheel.