I don't know either, but here's how to find out more
In cases of entirely unknown binaries, strings(1) is often helpful in getting a hint about what the file might be
strings /tmp/ics29586 | less
Have a look through the output and see if it's anything familiar.
Failing that, find out which launchd job it is being launched from:
launchctl list|awk '{id=$3; print "### " id; system("launchctl list " id)}'|awk '/^###/ {id=$2} /.*ics29586.*/ {print id}'
This should output one or more job tags in the form of (for example) com.apple.scrod (and a few errors, which you can ignore).
Once you have the job tag(s), get the launchd config for a job by running:
launchctl list com.apple.scrod # insert your tag instead
This (and the tag itself, which often contains an internet domain name in reverse notation) should give you some more information about what this process is. Feel free to post it here if you need further help.
Update: Forgot to mention this, but since it's a jar file, you can copy it somewhere and unzip it (jar files are really just zip files) and have a look at what sort of Java classes are in there.
Testing seems to show that the culprit is Intel's Turbo Boost technology, which disables processor cores on the fly without telling the OS. Since they aren't running the CPU idle process, activity monitor doesn't account for them, and it appears that the machine is under 50% idle when the reality is that it's near 100% idle.
At the moment it doesn't appear as though this can be easily disabled or controlled under OS X: How can I disable CPU throttling and CPU disabling?
Turbo boost is built into many Core i7 and i5 processors, and some of the latest Core i3 processors. You will have to check your processor version against intel's list of Turbo Boost capable processors to find out if yours has it. If you don't have sandy bridge, you probably don't have turbo boost.
Best Answer
The high CPU usage of coreaudiod is due to the ambient noise reduction software working (surprisingly, even when the built-in microphone is not in use).
Go to System Preferences > Sound > Input and uncheck the Use ambient noise reduction box.
Then, either reboot or run this one-liner to reload coreaudiod, and you should see coreaudiod CPU usage drop to 1% or less.