I doesn't sound like a military aircraft if it's a single engine plane. I would call the Portland Airport Noise Management Office. Here's the message I found on their website.
"19 days ago
North runway closed temporarily. All operations currently using the crosswind runway. Expect changes in overflights and noise. 503-460-4100"
However, that doesn't account for the noise during July and August. I left a message inquiring about this. I called this number to do so.
800.938.6647
Here's their office website link:
http://www.portofportland.com/Noise_Mgmt_Home.aspx
As a whistleblower, I'm willing to bet that tons of other people have the same complaint but didn't know who to call or what to do. They probably didn't make a formal complaint to this office. So, if you just take a little time to talk to them and express your concerns, then you'll be helping all of the other people this is agitating. I wish more people would voice concerns about these types of issues. Society would evolve quicker and things would change faster and for the better. I'm so glad you've asked for help with this.
Let me know if you need more help. I just shut down a construction company nearby for a noise complaint. They were using their bandsaw 12 ft. away from my bedroom window at 10pm. I spent about 20 mins on the internet and found out that the Department of Development has a rule that says industrial type work cannot be heard after or before Mon- Fri. from 7am-6pm, and absolutely no noise on Sundays.
If someone violates this you call in a complaint. First, the company gets a warning in the form of a mail notice and a phone call for violating code 18. If you complain again because they aren't adhering to this after they've been warned then they get an $8,000 fine. I also called the foreman of the project and told him what I intended to do. They tried to deny it, but I had sent a policeman out to tell the construction crew to leave and that he was my witness. I offered to fax their police report. That was all it took. VICTORY!!
Sorry for this long response. I just wanted to give you an example.