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Discussion Starter #1
Just asking if anyone has an identical issue? My ‘17 RGU has about 5k miles, still under warranty. When taking it in for the 5k service, I told them I hear an unusual road noise in the 70-80mph range. Hard to describe, but sort of a repeating rrr...rrr...rrr...rrr. Cycles about every half second. Sounds like an old 6 volt pickup turning over to start. Strictly engine or perhaps drive-train specific. If I let off throttle, instantly ceases, and instantly begins again when throttle reingaged. Not a noise from the pavement or from air flow. Dealer says they rode it and didn’t hear it. Just returned from a trip to Arkansas, and on the highway there and back, all I wanted to hear was the purr of that M8, but all I heard was rrr...rrr...rrr... Sure want to get resolved during warranty, and it would be helpful if anyone else who may have experienced this and solved it could give me some direction on what to say next to service dept.
 

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Sounds like it "could" be a loose exhaust heat shield clamp. They can sometimes set a harmonic vibration like that....easy to check...
 

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Tell ‘em it’s harmonic and it happens under cruising load at 70-80mph. Ask them to have it tested again, preferably with someone who has better hearing than the last guy who “couldn’t duplicate the symptom”, because it’s definitely making a noise, and it’s definitely obvious.
 

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I had this same type noise (I think from what your explaining) on my Fatboy with the TC88B, around steady 65 mph, started checking things and the Kuryakyn Tranny cover I had installed was left loose on one side after the dealer did some work, gave them all a twist and was good.

The RPMS and vibration thru the bike at certain RPMS can do this to loose panels, ect.. like others have said check around for loose items
 

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I had the same thing and I traced it to the right hand baffle in the exhaust. It had just enough clearance in the front to cause a harmonic rumble at 65-80 or so. I ended up isolating it by taking the saddlebag off and having my son literally step on the pipe causing it to flex and the sound to go away. I fixed it by mashing the front of the baffle into a slight oval shape making it fit tighter. Unfortunately most of these sounds are subjective to the rider, hard to trace and duplicate, and annoying as hell once you notice it. Good luck, I know it can be frustrating.
 

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Discussion Starter #7
Thank you for these responses. Harmonic vibration sounds like a good diagnosis, and also sounds like this could range anywhere from “that was an easy fix” to pulling out hair, but I’ll for sure scour the bike for anything needing tightening and see if I get lucky. Thank you all again for chiming in.
 

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I remember on the TC88 when they introduced the 6 speed- 5th gear had a harmonic whirl to it at a certain speed as well.... bugged the daylights out of most riders and it was traced back to the way the 5th gear was cut, which just caused a harmonic whirl..... good ole days!!
 

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Discussion Starter #9
So, for an update: Left RGU with dealer, and asked him to identify the harmonic vibration. He called to say he rode my bike in the 70-80mph range, and heard the repetitive noise. Let off throttle, sound goes away. Any other gears at same RPM, no noise. Slower speeds, no noise. He said he got on 3 other M8’s to run the same test, and found every one of them made the same noise. He has concluded it is an M8 related issue and is talking with MOCO. At least I’m not crazy. I don’t think you could hear it very easily if you are not wearing a helmet. He guessed it has something to do with the new cut of the gear, but it could be something else in this new engine that was done to make it run smoother. So, appears it may be some time before the official mystery is identified and resolved.
 

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OK, all you guys with M8's need to get out there and see if you can identify this sound under the same conditions, then report back! Very interesting.
 
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