Creaking pedals

I have a set of Shimano M540 pedals on my bike which has Ultegra cranks on them. Shortly after installing these they started to creak when I put some decent pressure on them. I had to take them to a LBS because I could not remove them with a short 8mm wrench. The shop got them off cleaned the threads, re-greased them and put them back on using a torque wrench to get the proper tension/tightness. After this the bike was silent, all was great. Fast forward to me washing my bike and going out for a ride the creaking returned. I'm not sure what washing the bike did if anything it could have been a coincidence or not.

What I would like to ask the community here is what is the remedy for creaky pedals. I don't want to put lock-tite or teflon tape on them or something like that but this drives me crazy.