About a month ago, my budget opened up at the same time I found a deal on a gorgeous machine. So I was about to join the HD family with a 2007 FLHPI (Road King Police).

It does not have the police solo seat, just a normal RK 2-piece 2-up seat. I do have the little air cushion puck thingy but I don't know if any of that system works at all (currently removed to fit the 2-piece seat).

As far as I can tell it's a bone stock Police edition 103", 26k miles. I recently swapped a local guy for some OEM slip-ons (it came with some non-branded loud pipes) trying to fix my ONLY gripe with it - helmet resonance. The quieter pipes are nice, but not a complete fix.

I ride ATTGATT. Boots, pants, jacket, gloves, helmet and earplugs. I have found that between ~1900-2800 (has a tach) rpm under load it resonates though the seat JUST RIGHT to rattle my helmet into my earplugs; like someone is boxing my ears. If I scooch my tailbone back, and slightly onto the pillion pad, it goes away. I've tried an air pad that I had from my last bike (no dice). But if I do my air pad AND a folded bath towel it seems to help tremendously.
I currently have the supplies to mod my seat myself. I have a gel bicycle seat cover and 2" memory foam from the fabric store. My current plan is to pull the cover, carve in a slight depression to house the gel cushion; then cover the whole mess with memory foam before re-installing the vinyl. (I've done similar on an old Honda and had good results regarding comfort, but it didn't have the resonance issue).

If that doesn't work; I have been researching the gel-based Saddlemen seats (RoadSofa and similar). Has anyone else had a similar issue? And did a nicer seat help?

I don't believe I have any mechanical issues. Front motor mount is a new Drag Specialties unit. Compensator/primary doesn't make any ugly noises. Starts up easy, shifts easy, pulls nice and hard, smooth as butter at 3krpm and up, fuel mileage seams about right, etc. I get it that they're paint shakers at idle. The last HD I ever road was a 2017 at a demo day and they were absolutely glass smooth; but that's the newer (relative to my 07) Rushmore chassis and was a 15 minute ride, a LONG time ago

 

I get the same issue on my old Softail, the helmet becomes a speaker amplifying the mechanical sound (stock exhaust, and I always wear ear plugs).

If I lift off the seat the sound is gone.

The seat on my Softail is original, there is probably little cushion left, maybe it is because I am essentially sitting on the frame...

 

Glad to know I'm not crazy (about that anyway).
Other things I've tried:

I've gone with AND without the windshield - same symptoms
No earplugs - resonance is gone, but speeds > 40 mph are miserable for wind noise
I've tried different earplugs - I usually wear the Howard Leight 33db orange ones. I've tried a knockoff "eargasm" clone "Hi-Fi" earplug. They don't like to stay in; AND they still have the resonance. Neat idea though. Might try the Alpine MotoSafe at some point
I've tried some foam plumbing insulation on the frame rails under the seat but no real difference.

Same thing with lifting off the seat - noise disappears as soon as my tailbone has any air under it.

Honestly if I can't solve this issue I won't be able to keep the bike because it sucks to ride for more than 30 minutes or so.

 

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A couple things to try, an AirHawk seat pad or maybe a different helmet. I had a resonance issue (11 RK) but got rid of it with OEM mufflers...

 

Done both of those. Modding my oem seat in the next day or two. I've had some makeshift dumb stuff help (airhawk + folded towel) that makes me think I can solve it.
I don't mind spending on a good seat if others have had success there; but dropping a fistful of Benjamins to get no improvement would be frustrating.
I've thought about a new lid too but same issue as a seat - spending money to potentially not help would suck. It ages out next year anyway.

 

DO you have the windshield on the bike? If so see if adjusting the tilt of the shield adjusts the sounds.

 

Try a sheepskin cover from Alaskan Leather. May help dampen the sound.

https://www.alaskaleather.com/

 

Happens with or without the windshield. Appears to be strictly rpm related because I get it at any speed in that 1900-2800 rpm range.

I was able to try a friend's 08 RK (stock seat) and his did it for me too.
​​​​​​​I did most of my mod last night, if that doesn't get it I may give one of these a go before shelling out for a seat. Tyvm!

 

Call Mean City Cycles. I bet they have solved this problem before.

 

I'm sure they use better materials, but in concept that's actually what I'm doing myself - adding a gel layer underneath and memory foam on top. I didn't reshape the OEM foam but I didn't have any actual comfort complaints aside from the resonance in my helmet. Honestly I'm just trying to alter the resonant frequency enough so I can cruise at the bike's favorite RPM range.

I'm about $45 in materials in cost so far, but I ran out of staples to put the cover back on. Going to get some more today and try to give it a spin and let everybody know if I had any success.

I haven't replaced the swingarm isolators yet, but it only has 26k miles even though it's 16 years old. Not sure if it would help or not; but there's not any more movement in the motor than expected, and the swingarm doesn't have any noticeable play so I assume they're basically fine.