plastic pipe coming out of wall is really loud
It's a direct-vent (a.k.a. powervent) water heater exhaust. My home has the same thing. The first night I slept there it about knocked me out of bed, and now we usually keep the window closed on that side. 

You can find duct mufflers that will dramatically reduce the noise, but they're something you'd need to work with your property owner to install safely and according to building and rental codes. You're dealing with carbon monoxide, so you don't want to take risks.

Another option might be to route the pipe up the wall and above the roofline, or simply to direct the opening away from windows. Again, this would require homeowner approval and assistance, and you need to prevent rainwater intrusion.