You would need to obtain logs from your hosting provider about who/what/where. As they can't really expect you to resolve an issue without providing you with diagnostic and information first. You would need to know what process is running or spiking, is it PHP, MySQL or something completely unrelated to our software. Once you have that information, if it's PHP, you need to know the file being executed. For MySQL, you need to know the query which is being executed (such as from a Slow Query log). Etc...