Bit of an esoteric question - how do I stop debug messages from being written to the serial port?

I'm trying to use the serial port of my PC (/dev/tty.serial0), but the computer keeps sending garbage to it every few seconds. When I set the baud rate properly I can see what's being sent, and it's messages that look like this:

tx_flush:1028: xid 34218 tx status: #1260 finish 1241 enter 2484 wait 28 16011us close 284us flush 26654us

The tx status: #(number) finish (number) both increment by 20 each time. The other numbers are usually the same, but sometimes different and I haven't been able to spot a pattern.

I occasionally get other messages, such as set_maintain_dir_size: 18580: will chain updates on 12885611454 back up to dstats-key: 12885200327. But it's almost always the tx_flush stuff.

So I don't know whether this is a macintosh problem or a hackintosh problem but my question is does anyone know how to turn it off so I can use my serial port?

Thanks :)