Can anyone help identify this noise when accelerating?

[chonkuszz]

Hi, wondering if anyone is familiar with this crackling/popping/knocking noise when accelerating (50kW on the power meter seems to be the sweet spot) in my 2006 GS450h, 89,500 miles.

I have had a good look underneath the car for anything loose or rattling around but have had no luck pinpointing this.

I can only rev. up the engine to around 2000rpm when in inspection mode at a standstill, and when using S mode with engine braking, the engine can rev quite high up to 5000-6000 rpm but the noise still cannot be heard. 

Only when accelerating reasonably quickly can the noise be heard. Sounds like it is coming from the front somewhere or perhaps underneath. I've tried using a full tank of Shell 99 V-Power in case of pinging or detonation, but no change.

Is anyone familiar with what this could be?

[Mr Vlad]

Not knowing this model but that could be a loose exhaust shroud. Get your cat on a ramp and check them. It's quite possible they've become loose or a bolt has rusted making the shroud loose.

[chonkuszz]

I did recently take it to my local mechanic, we got it in the air and had look underneath, we think it could be where the Propshaft mounts to the gearbox. There's a slight knock when you rotate it by hand. He reckons it's fine to drive for now and got it booked in next month for him to have a deeper look.

 

[Mr Vlad]

There will always be a little play in gears. Where the prop shaft joins the gearbox and a slight knock is heard when rotated by hand is normal. 

If it was indeed a very worn coupling then the noise heard when driving would be a constant ratatat type noise. 

The sound on your video is not constant. 

I'd be intrigued what your mechanic says when 'he' has a deeper look.

[chonkuszz]

Well, we put a new prop on from a low mileage Crown import, same part number.

The new one is in and was in much better condition but, lo and behold it did not solve the problem.

I still enjoy the sound of popcorn upon brisk acceleration... The search continues.