1998 Toyota Camry - Shaky when wet

Maintenance/Repairs
1

Driving automatic 6Cyl 1998 Toyota Camry 178K miles on it.
Apart from regular maint/repairs (I.e. struts, brakes, alignments, battery (incl terminal/cables), and timing belt (@ ~98K miles), this care runs beautifully! Unless its raining…
When its raining, it will start fine. And run fine… for a while.
After a while - this will be at 35 mph or 60 mph - it will sound like its over-revving or out of gear, but the RPM does NOT change.
I take my foot off of the gas pedal for a moment, noise stops.
I try again a second or later and it makes the same noise so I repeat
After doing that two or three times, the noise stops and it will drive fine.

I can also feel a slight shaking/knocking in the gear shift (my hand resting on it) while the noise is being made.
None of this happens when its dry

Wondering if this is signs of the tranmission going… water getting in the gear box… dont want to sink too much more money into the car at this point

Any and all help/advice would be greatly appreciated

2

"…it will sound like its over-revving or out of gear, but the RPM does NOT change. "

At this point Click and Clack would say, “Doesn’t anybody screen these calls?”

You might want to take a passenger along to watch the tach while you drive to see if the RPM is doing anything during an episode (besides drop when you take your foot off the gas).

3

Have you ever changed your spark plug wires?

4

Not the original owner. Inherited from wife’s grandparents ~6 years ago (~75K miles at the time). Since I started driving it, the spark plug wires have not been touched.

5

This car has 3 coils and 3 wires. The wires go to the rear plugs. I would suspect the wires. Also, these are dual electrode plugs, because each plug fires twice as much as it would if it was single coil on plug. Another words, each coil fires 2 plugs simultaneously.