Sounds perfectly normal to me. I've been listening to mine for 3 years now, 7 days a week. I'm starting to think that these little 4 bangers are almost organic creatures. Each one having it's own particular tone or pitch and timing. I must say, since ULSD mine has sounded like crap under load. Still have the same power/torque which is confusing. I mean, I climbed a short familiar hill today using 4th where I've always used 3'rd before. Kept the same speed as if I were using 3'rd. So many things have happened at once this year, i.e. frigid temps/ULSD. I'll hold out till spring and see what happens.

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1981 240d
Newport,RI