Think I know what you mean.....like a sharp/tight ache?
Before I was induced I was hooked up to the heart rate monitor thingy and the sound was down. The midwife came in and she asked if I was alright and I just said I couldn't get comfortable because I kept getting a funny pain in my back. She sat with me for a while and told me to tell her when I got the pain.......turns out I was having little contrations but just thought I had a bad back!
I'd actually been having them a couple of times a day for weeks but I just assumed it was a sore back from me being so incredably HUUUGGGGEEE!!!
At least next time I'll know!!