Relay problems

[RonnmarkB]

Good day

I have built two of theese shakers, however I have encountered some problems. On both builds, the timer isn't consistent. Once activated, the shaker may run for 2 or for 5 seconds, this issue appears to be random. Once in a while the relays also "clicks".

For example, switch is triggered and run time on vibrator may be as follows (timer is not adjusted in between)

2s
1,5s
4s
0,5s
2s
etc

Do you have any idea why I'm having this issue? I'm using 5,1k ohm and 220uF.