I have a weird pulse in my thigh on the right hand side of my knee. Could this be a muscle spasm? Or is there something wrong?

Popliteal aneurysm . The only pulsating object in proximity to the knee is the popliteal artery. Usually this is not easily felt. If it is then it may need further evaluation with an ultrasound, especially if you have a history of other aneurysms.
Get checked. Ultrasound will give answer usually. Easy test.
Unsure. I suspect that you need to see a vascular specialist as this is not normal and needs to be further evaluated.