My road bike is making very noisy popping/flexing sounds when pedaling. There are multiple sounds in a semi-regular pattern with each pedal stroke, and I can feel extra movement through the pedals as I hear the sounds.
The sounds are most pronounced at moderate intensity and still present at light intensity, but when I do a hard sprint or threshold effort (i.e. when the drive-train is under constant pressure) the sounds disappear.
Also, if I grab a pedal with my hand and press my weight down on the crank, I can feel some give and hear a sound as I do this.