Hi,
I’m afraid there is no way to tell for sure. If the excess usage were from database queries, or there were specific queries taking a long time, that way there is maybe a chance to tell, but based on PHP process usage there is no definite way.
Just to be sure, I would recommend going throught the performance tuning section of the documentation to make sure the search is configured optimally. I strongly suggest using the index table engine and the cache – in case of resourceful queries on the database it can alleviate a huge amount of load.