I'll preface this with an IANADBA because i really am not.

Every day, at up to 5-10 seperate times, our Oracle 8i server has a process which begins allocating memory and will not stop until it reaches about 25% of the server's memory. This takes about 2-3 minutes usually and makes Oracle entirely unresponsive.
Code:
32076 oracle    15   0  161m 161m 161m S  0.0 16.1   0:03.78 oracleCCDBS (DESCRIPTION=(LOCAL=no)(ADDRESS=(PR
We can replicate this behaviour by starting Toad on a machine, this will lock up oracle for a while too. This is a serious issue for us as response time is far more important than efficiency. We simply must have queries back within 2 seconds and this problem is causing us a fair amount of damage commercially.

Obviously we'd hire an Oracle DBA to sort this out if I had any say in the matter, but I don't and this is a very old system designed by someone I suspect was not amazingly familiar with indexes. I have various scripts to list locks, list running jobs and even grab the SQL text from running processes but when this issue arises, oracle will entirely lock up.

I'm at a total dead end here, I desperately need some way to identify what is causing these bizarre allocations and I cannot take this database down for more than an hour in the middle of the night.

I prostrate myself in front of you real DBAs and humbly request someone stop me getting fired (yep i'd get fired for his mistake, charming eh?)