Unable to determine issue

For at least the past year and longer during a cold start of my 2009 Toyota 4Runner V8, a thumping sound comes from the engine bay. It last for at least 30 seconds and longer, but goes away when vehicle goes from Park to Reverse. I have had it in to a mechanic shop multiple times but they can not determine the issue. Any thoughts/ideas?

I tried to upload a video captured on my cell phone recording the noise, but got an error stating the forum site does not accept MP4 file format.

 

It might help to upload a video so we can hear the sound.

 

Welcome

 

welcome

 

welcome

 

What video file format does this site accept?
Thanks.

 

how do your motor mounts look?

 

None. Need to upload the video to an external site (YouTube, Vimeo, Imgur, Instagram...) and post the link here.

 

Post it on YouTube and then provide a link. It is what I do

 

Motor mounts were checked by local mechanic shop with no issues observed. I will attempt to post captured video and provide link. Additional information - the thumping/knocking noise at cold startup is rhythmic in nature, which points to some part/area associated with idle engine rotation. Not being mechanically knowledgeable, besides the transmission being engaged what other systems get involved when vehicle is put in reverse or drive at which time noise goes away?

 

Have you had it to the mechanic at a time where they could replicate the noise or hear for themselves? Also, mechanics' stethoscopes are inexpensive and might help you isolate the noise.

 

It could be as simple as a pulley going bad. Get a stethoscope from autozone and do a quick check up on those pulleys and other places. Post some pics so folks can help you out a bit more.

 

Yes mechanics heard the noise once during 3 attempts to replicate. I will look into the stethoscope idea and do more investigation on my own first. As for pulleys going bad would such explain the noise going away after coldstart in Park and shifting into Reverse or Drive? Thanks for all the recommendations and help so far.