Loffen Messages: 1087 Registered: August 2013 Location: Norway
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Senior Member
Just thinking here, if you have a Harley sound could it not be one of the exhaust manifold gaskets ? I do rarely see a dunut failure on the GMC but a lot of blown manifold gaskets..
1973 23' # 1848 Sky Blue Glacier called Baby Blue and a 1973 26'-3 # 1460 Parrot green Seqouia Known as the Big Green,
And sold my 1973 26'-2 # 581 White Canyon lands under the name Dobbelt trøbbel
in Norway