Knocking Noise From The Rear?

[DayWalkerSC400]

Hello everyone,

I have a 2006 IS 350 and recently I have been hearing a strange noise. It seems that around highway speeds (between 55 to 80+mph) I will hear a strange knocking sound from the rear whenever the road is a little bumpy. I cannot pinpoint where the noise is coming from exactly. However, the noise sounds just like something hitting the rear windshield. It really sounds like the brake light from inside the rear windshield is hitting the rear windshield whenever I go over a bump. Is this possible? Or is the noise something else? I am just trying to figure out what this is and how to stop it as it is really getting on my nerves. Does anyone else have this experience as well? Thanks in advance for the help!

[13IS250C]

Something loose in the trunk? Spare tire and all the tools secured properly? Maybe something loose in the exhaust system?

[clubfoot]

If you have the privacy screen, raise and lower it :)

[LEX-SV]

Does your car have F-sport lowering springs on it?

The early versions of those springs caused clunking noise from rear. A revised spring came out later eliminating the noise.