Grinding/Clatter Noise from Engine Bay at Start Up

[09GrigioTSX]

Over the past couple months my TSX has been making a loud clatter/grinding noise immediately after start up. This only seems to occur after the car has been sitting for a bit of time. It seems to only do it after sitting overnight in the garage or sitting in the parking lot at work all day. My first assumption was it may be an oil starvation problem, perhaps in the valvetrain or something? At first I thought turning the key to the "on" position would allow the oil pump to prime and would help, it did at first, but now nothing helps and it does it every time no matter what.

I check my oil regularly and have changed it once since I've owned the car. I changed it at 20% oil life the first time and it currently has 30% oil life.

I'm brining it into service tomorrow, but wondered if anyone else has heard of this issue or has any ideas what it could be?

Thanks in advance for your help!

Dave