GTi6 noisy in wagon mode

[TrinityJayOne]

Cramming my MTB into the back of the GTi6 requires conversion to wagon mode, like so-



I've noticed though that when I do this the exhaust resonates/drones from about 2,000rpm all the way up to whatever I care to rev it to. At first I thought it was the bike frame amplifying the vibrations from the boot floor, but after today's ride I had the bright idea of going for a drive with the bike removed - exactly the same. I wouldn't have thought the parcel shelf and rear seats offered all that much sound deadening, but evidently they do. To clarify, externally the exhaust sounds identical, it's only internally that it sounds odd. It's more annoying than loud, makes it sound like I've got one of those 'Milo' brand exhaust systems you see on Civics & Skylines.

So, any ideas on how to combat it? I know a bike rack is always an option but I'd prefer not to have a towbar installed for obvious aesthetic reasons! Perhaps a custom foam liner or something?

[Slam Wagon]

Sound proof the boot, like you would if doing an audio install. Plenty of info on the forum about the stuff.

[lolsteve]

There are some holes in the boot floor/no sound deadening on it and the parcel shelf, rear seats kind of both acts as a sound deadening box around it.
I've removed the rears out the zr and you can hear the exhaust so much more on it, it's quite nice for when you're just going for a blast

[Piggy]

Can't hear myself think with my back seats down!

[Slam Wagon]

No back seats so its just normal for me although the false floor does make a huge difference.

[Eeyore]

cloud 9 carpet underlay...

[TrinityJayOne]

Update! All fixed up now I'm happy to say.

I visited a local foam supply company and got a large sheet of foam cut to size, about 2" thick. It fits snugly in the back when the seats are folded down, then when I'm done carting my bike around I just lift it up and pull it out. Easy!

Without the foam in the back I was getting up to 84dB when I slowly revved to 4,000rpm. With the foam sheet added it peaked at 80dB. Still a touch louder than with the seats up & parcel shelf in but the resonance/droning is gone. Don't have to worry about getting my bike clean before I chuck it in anymore either!