2015 Honda Civic Mystery Issue - Metallic Rattle in Drive @ 1500rpm + High Pitch Idle Rattle

By civic15 10 hours ago

Question

Hello, I have a 2015 Honda Civic EX (automatic CVT) with 137,000kms. An issue started a month ago with a metallic rattle and I'm stumped. It seems very loud when driving by buildings with the passenger window open

The Noise Only Occurs:

While cold/warming up, until it reaches operating temperature. The car sounds fine once fully hot. Also seems to be less severe if the outdoor air is warmer.
In drive only, though if I spike the RPMs moderately in park/neutral I can catch it for a split second. Otherwise no rattle when revving in park/neutral.
Only in the rpm range between 1200-1700rpm, under acceleration in drive and when crossing back down through the range.

Here are some clips of the noise, it's hard to find others with this issue and unlike my situation, for these individuals it was the tensioner:

https://www.youtube.com/shorts/Lk7mEz_qfVY

https://www.youtube.com/watch?v=Z-_1iax3gsg

I took it to a very reputable mechanic who is also stumped. This is what they tried:

Taking the belt off and running it on a hoist under the conditions above (left overnight, in drive, accelerating to 1500rpms). The noise went away when the belt was removed, came back with the belt on.
They replaced the serpentine belt tensioner twice (first with a Dayco then switching to OEM), replaced the belt, and idler pulley. The noise didn't change.
Apparently ruled out AC Compressor and Alternator, though I'm still suspicious about that. They think it is the water pump but they aren't sure.

Accompanying the noise is a high pitch whine sound coming from the front of the engine, please see this persons reddit post below for a perfect example. This noise, unlike the rattle, occurs in idle, can often be "aggravated" but revving into the 1-2k rpm range, appears quite quickly after starting, and goes away entirely when warm. Possibly related??

https://www.reddit.com/r/MechanicAdvice/comments/1f6kmet/high_pitch_whine/

Thanks so much, I truly appreciate your help and expertise

scottykilmer · Answer

Here's the thing noises can be pinpointed. See my video finding the source of car noises. Then either buy one of those machines or find a mechanic who is a real mechanic and has such a machine. That will definitely pinpoint the noise and since it goes away when you take the belt off it has to be something. The belt thrives. And it would certainly be bizarre if it was the tensioner cuz if they use say a cheap aftermarket tensioner they often make noise but you really have to pinpoint it