2010 a bit "boomy" over bumps?

You know, I have really been noticing lately my Prius III is quite boomy over bumps... Like reverberation coming from the back-end of the car in the spare tire area. This makes its way all the way to my head as bass.

Ripples in asphalt at low speed or small ridges in roads at low speed make it really apparent.

Does anyone else notice this?

 

I was coming from a very stiff Mazda Protege beforehand. (A 2001) That car had lots of bracing in the rear of the car and was very stiff, so zero booming.

But I never noticed the booms when I first got the car or test drove it, but it's super apparent to me now. I just must not have been paying attention at the beginning....

I think I'm going to take out the spare tire and tray and see if that changes anything. I keep the cargo cover stowed -- I wonder if being closed over the cargo area actually helps contain some of the sound?

It's not a huge deal ..... but I've owned a CRX and Civic wagon in the past (way in the past) and those cars had no booming..... so it's not like all hatchbacks do this.

 

Ya, I know it's not the tray being unseated. I took it all out to inspect the spare tire a while back and I'm sure it's all in there right. I also have some stuff in the tray and put some anti-skid rubber down.....

I thought about the tire pressure too -- having tried 44psi and now the 34 I normally run ... Didn't seem to make a difference, but I did notice if I opened the back door of the car and stuck my head in then kicked the rear tire, it booms really loudly.