Denver -- strange sound in sky on Jan. 25, 2012

I'm just now able to get around to posting this. This was mid-week and at around 9 a.m. I opened my door to my porch and heard a continuous rumbling sound in the sky, kind of like a jet passing overhead. It lasted for at least an hour. I even checked planefinder.net and did not see much traffic and when it got loud, planes were nowhere near Denver.

I know lots of people from Denver are on this site, so did anyone else remember hearing this? Thanks!