I had the flex pipe at the end of exhaust manifold replaced by a local welding shop because it failed annual inspection. The shop cut the old one out and welded in a new one. They also patched up the muffler at the back for me. The car passed inspection after the repairs, but I started hearing this high pitched noise when accelerating or otherwise under load. If I ease off the gas the noise stops and if I step on the gas it will come back and stay there while the engine is under load. Very strange and difficult to find since it does not do it at idle (no load) or does it so little while raising the idle momentarily that it's impossible to pin point. I also got a Check Engine Light on, but my older OBDII reader shows no codes. I can clear the light and it goes away for a while, but then comes back again with no readable codes. I will go to a local auto store and ask them to read the codes with a newer reader. Perhaps mine is just not getting some of the codes that are Volvo-specific. the car seems to run just fine. Strong acceleration, no hesitation of any sort, the gas mileage seems normal, though I have not had a chance to measure it much since the exhaust repair and appearance of the noise. any clues out there? I am all ears.

Thanks!
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Vladimir. '98 S70 base, 5-speed manual - his, '93 945 - hers