Turning on wireless slows down wired networking

I have a WL-500W using firmware from https://code.google.com/p/wl500g/. It is only used as a wireless router, with the main router and my computer both connected to the LAN ports. The wireless is normally off, and I only turn it on when I need it. On two occasions, I had problems streaming video to the TV via wired Ethernet when wireless was turned on. When I turned off wireless, the problems stopped. No authorized users were using wireless at the time.

I wonder what's going on. I don't think someone hacked into my network, as it's secured via WPA2-AES, a weird password, and hidden SSID. However, I don't know what else could be going on. The wired Ethernet signal should just be going through the switch chip in the router, and wireless shouldn't be affecting it.