Well I already posted a WhoIs on trls32.net . Doesn't tell me a lot.
The requests go out, from a PC, between 1 and three times per day but during the time I'm using the machine. Yes that box has Wireshark on it but it has not been running at the time. I don't see any Wireshark related services running.
I do have Wireshark running today to see if I can capture packets directed to TCP port 61899.
FYI I see no port 61898 inbound or outbound stuff (both would be blocked) in my logs. -- Don't feed trolls--it only makes them grow!
I doubt a Riverbed steelhead would have local access to a computer unless you were administering the console for it from that box. However you hint at not being aware of a Steelhead on your network.
The only other item for that port initially seems to be: Xsan is Apple Inc.'s storage area network (SAN) or clustered file system for Mac OS X
Guess Wireshark will at least give you a little more info. -- The only thing necessary for the triumph of evil is for good men to do nothing - Edmund Burke