I have an 08 MDX that has just recently started to making a muffled clunking or knocking noise that is coming from behind the dash. I most frequently notice it right after start-up in the morning or sitting in traffic / stopped with car in Drive. It happens with the HVAC on or off, but sounds like it is related to something with the HVAC. AC blows cold and everything seems to be working fine with the HVAC, so maybe not. Of course, I can't reproduce it for the service writer. Anybody experience this or know what it is? I have 113k miles on the MDX. Thanks!