Clunk sound when engine engages 2015 Prius V

Check the condition of the half-shaft boots - torn or leaking. You may have an issue with the flex plate that connects the engine to the transmission. Unfortunately, you'll need to remove the transmission to replace it. Hopefully that's not the issue. Take it to a professional, experienced Prius mechanic, for a proper diagnosis.

Good Luck......

 

No expert but there's a damper plate twixt motor and planetary gear. Think I've seen it can have issues.

 

I doubt that's a significant problem, unless it suddenly became a lot more noticeable. Due to backlash, there can be a slight "clunk" any time the direction of torque reverses on gears or joints.

 

Trani might be getting bad................. I had to replace mine..... clunking was the first thing I noticed

 

Transmission don't "go bad" unless you run them out of fluid from a leak or something. I've seen these flex plates that were put back in after an engine swap clunk more and make more noise after someone drove the car a long time on a blown headgasket with many many cold start rattles and shakes. Misfires with the shaking puts stress on that flex plate and damages the pressure plate and springs over time.

 

Wow i didn't know you were with me in the car and serviced my trani.........
Never (drove) it with a bad headgasket.......... no leak......... the noise was long before junk headgasket replacement
But I have personally replaced the
Inveter
Transmission
Brake System (firewall)
Head Gasket
Water Pump
Traction Battery
Have you?

 

I don't have to be with you in the car and service it, your mechanic just took you is all.

 

There is no cv belt in a gen3 or newer Prius. The planetary gears are always engaged. One of the electric motors in the transaxle synchronizes rpm through the planetary gears to allow the engine to stop while the car is moving.

The most common reason for a loud clunk or rattle when the engine starts is a misfire caused by a leaking head gasket.

In early stages it only happens on cold starts but later on it can happen every time the engine turns on while driving. Usually most noticeable when taking off from a stop. Primarily due to reduced road noise.

The noise comes from the damper due to a lack of sync between the engine and the transaxle. Caused by a misfire. Normally the damper is fine once the misfire is eliminated. A head gasket misfire is coolant fouling of the spark plug. That fouling is quickly burned off and typically does not last long enough to cause a check engine light.