Yes, you are right. I'm from the northwest of England, and there's a peculiarity in the speech of that region with regard to final 'ing' sounds. In standard English, the end consonant of a word such as "sing" is a nasal /ŋ/ : basically a 'n' in the nose, followed by a slight 'stop' representing the lightest of 'g' sounds. But people from northwest England generally add an extra /g/ after the /ŋ/ which often carries on to the next vowel. This means that 'singing' sounds like 'sin-ging', and 'hang on' like 'han-gon' in the pronunciation of people from Manchester and the surrounding area. Is that what you were thinking about?

In standard English, <ng> is not /n/ /g/ but a separate sound /ŋ/ as mentioned by Su.Ki. Some dialects add a hard /g/.

Yes, it might because of accent. Also we often connect words together when speaking quickly, so perhaps if it is the last word in a sentence, or sentence that is being said slowly, you may be more likely to hear it. The other possibility is that people are choosing to say one word with greater emphasis (stress/intonation), because these sort of decisions can alter the meaning of sentences.