Either the timing belt is off 1 tooth, the cam position sensors is dying, or the CVVT solenoid on the top of the Tbelt housing is dirty and needs cleaning.
The CVVT solenoid is my first bet, it is oil pressure driven and dirty oil and/or cold engine running can clog it up. It will require an new gasket if removed and I understand the dealers have an upgraded version that works better.
You should remove the Tbelt cover and check the timing marks, belt, rollers, etc just to be safe anyway.
Klaus
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Volvos should be saved from the junk yards, not donated.
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