The 450SEL would do the same thing when it got cold. Sudden loud noise as speed increased, not going away until speed was near zero. Speedo needle didn’t look like it was affected at first glance but if you watched it, you could see something was up. A bit of flutter that wasn’t normal if I remember right.

The inner core of the cable can start oscillating in the housing due to lack of lubrication. No amount of cussing or banging on the dash will fix it, it must be properly lubricated.

Michael