Answer by taking a quote from the following article:

The Vedic period or Vedic age (c. 1500 - c. 600 BCE) is the period in the history of the Indian subcontinent intervening between the end of the urban Indus Valley Civilization, and a second urbanisation which began in c. 600 BCE. It gets its name from the Vedas, which are liturgical texts containing details of life during this period that have been interpreted to be historical and constitute the primary sources for understanding the period. The Vedas were composed and orally transmitted by speakers of an Old Indo-Aryan language who had migrated into the northwestern regions of the Indian subcontinent early in this period. The associated Vedic culture was tribal and pastoral until c. 1200 or 1100 BCE, and centred in the Punjab.

The commonly accepted period of earlier Vedic age is dated back to the second millennium BCE. After the collapse of the Indus Valley Civilisation, which ended c. 1900 BCE, groups of Indo-Aryan peoples migrated into north-western India and started to inhabit the northern Indus Valley. The Indo-Aryans were a branch of the Indo-Iranians, which--according to the most widespread hypothesis--have originated in the Andronovo culture in the Bactria-Margiana era, in present northern Afghanistan.  Some writers and archaeologists have opposed the notion of a migration of Indo-Aryans into India. Edwin Bryant and Laurie Patton used the term "Indo-Aryan Controversy" for an oversight of the Indo-Aryan Migration theory, and some of its opponents. These ideas are outside the academic mainstream. Mallory and Adams note that two types of models "enjoy significant international currency" as to the Indo-European homeland, namely the Anatolian hypothesis, and a migration out of the Eurasian steppes. According to Upinder Singh, "The original homeland of the Indo-Europeans and Indo-Aryans is the subject of continuing debate among philologists, linguists, historians, archaeologists and others. The dominant view is that the Indo-Aryans came to the subcontinent as immigrants. Another view, advocated mainly by some Indian scholars, is that they were indigenous to the subcontinent."  The knowledge about the Aryans comes mostly from the Rigveda-samhita, i. e. the oldest layer of the Vedas, which was composed c. 1500-1200 BCE. They brought with them their distinctive religious traditions and practices. The Vedic beliefs and practices of the pre-classical era were closely related to the hypothesised Proto-Indo-European religion, and the Indo-Iranian religion. According to Anthony, the Old Indic religion probably emerged among Indo-European immigrants in the contact zone between the Zeravshan River (present-day Uzbekistan) and (present-day) Iran. It was "a syncretic mixture of old Central Asian and new Indo-European elements", which borrowed "distinctive religious beliefs and practices" from the Bactria-Margiana Culture.

What were differences after inhabiting the northern Indus Valley?
"a syncretic mixture of old Central Asian and new Indo-European elements", which borrowed "distinctive religious beliefs and practices" from the Bactria-Margiana Culture.