If it's not affecting the overall performance of the car mate then I wouldn't be overly concerned about it myself, electronic injection makes a lot of noise on engines too and along with emission control valves etc etc ..... they tend to make a variety of noises. In the meantime just drive it and see. If the Ford service dept. say it's normal operation and you're concerned about it ask them to put it writing for you, then if there is an issue you will have something to document that it was checked by them and passed as OK
For what it's worth, I'm sure most people have been or will be in a similar situation at some stage of owning a car and it can be quite daunting especially when finances are tight, I've been there and experienced it myself but if you start to worry about every single noise or rattle or squeak you hear you will never be able to relax and enjoy the ride :( I have now adopted the attitude that " If it aint broke don't fix it " and if and when it does worry about it then