Q: Blockage in crankcase ventilator on 2002 Volvo V70

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Problem occurs after car has been driven about 3 miles and is noticeable by a noise like a squeal. Noise stops when oil fill cap is removed. Car has 105,000 miles.
(1) Answer
This may be a blockage but more likely a vacuum leak at one of the hoses under the intake manifold. under the manifold, near t he alternator there is a vacuum hose, check there and see if it's split. Replacing it is very difficult and I would suggest anyone but an experienced mechanic remove the intake manifold and replace the hose.
Good Luck