Spike in click rates lately

Has anyone else experienced a spike in click rates over the last few months? We had a click rate for all emails that would reliably come in around 2-3% for years, then in the last 3-4 months we are seeing click rates of 15% all the way up through 53% (typically coming in now around 35-40%). This is completely inexplicable as our contacts/audience have remained largely the same, and our emails are largely the same. I feel there must be a change either in the reporting that is mistaken, or in the way clicks are being counted. Has anyone else seen this? Any suggestions as to an explanation?