noisy electric heaters

What exactly is the type of noise here?

Because an electric heater should make no noise at all!

Possibly a click of a relay switch when it turns on, but that shouldn't be very loud.

If it's the type with a fan to distribut the heat, then the fan can make noise. If so, the usual problem is that the fan needs to be cleaned and lubricated.

the heater is your standard baseboard heater and whenever it cuts in to heat a room i can hear a knocking/clicking/pinging sound which is quite loud and goes on and on and on. That's the best way i can describe it. Should i just replace the heater altogether?

Two possibilities to check out:

1. It's dirty & dusty under the cover, and when the element heats up, it burns that dust away, which gives a popping or crackling noise. (But this usually ends soon, and I've not heard of it being loud enough to wake a sleeper.)

2. The heating element has come loose from some of the brackets that support it along the heater. So when it heats up, it stretches and moves and makes noise. Again, I don't think this would be loud enough to wake someone.

This is more serious than the first one. Possibly the element can be re-attached to the brackets, but it may be a sign that the unit is reaching the end of its' useful life, and will soon need replacement.

Frankly, neither of these seem very likely to me, but they are possibilities that you can check out.